package com.justnow.offer;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Scanner;

/**
 * @author justnow
 * Created on 2020-10-02
 * Description
 */
public class Shenwang02 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String s = scanner.nextLine();
        HashMap<Character, Boolean> map = new HashMap<>();
        char[] array = s.toCharArray();
        for (char c : array) {
            map.put(c, !map.containsKey(c));
        }
        for (char c : array) {
            if (map.get(c)) {
                System.out.println(c);
                break;
            }
        }
    }
}
